The former Daily Mirror editor told Press Gazette: “I only agreed to six months and I will have done it for exactly six months when I did my last one this week.

“It was an experiment to see whether they could draw people to the IPSO website and in truth I think people came to read my column but they didn’t hang around to see more of the site, so from IPSO’s point of view it didn’t really drive the traffic they wanted in the way they wanted.”

An IPSO spokesperson said: “IPSO has really enjoyed publishing Roy’s work for the last six months. Hosting external blogs from commentators like Roy, whose observations on the media are second to none, is an important part of our external affairs programme.

“However, we’ve mutually agreed not to extend the contract but are grateful for his work.”

Greenslade told Press Gazette that as well as ending his IPSO blog, he will step down from lecturing at City University, where he is a professor at its Department of Journalism, in March.

“I think there comes a time when you say enough is enough and I have said it and I’m very relaxed about it,” he said. “I think I have had a fantastic career. Fifty-three years as a journalist – it’s enough.”

The 70-year-old said he was going into “structured retirement” but would continue writing for the Guardian once a month until March, when his year’s contract will come to an end.

He said he would be happy to continue writing for the paper, but added: “The Guardian will be undergoing a big change because it will be a tabloid. None of us know what the future holds.

“I have worked for the Guardian since 1992 and I love the paper and hope that continues, but they are desperate in terms of money and I shouldn’t think they would want to go on paying someone who is marginal.”

He also said he was a “great supporter” of Press Gazette’s Duopoly campaign calling on Facebook and Google to stop destroying journalism and pay more back to publishers.

“I still think this is the most important time in history of the media to ensure that it holds to account the big companies and so on… I’m terrified for the future of journalism,” he said.

“I’m giving a lecture in Edinburgh University in November about ‘Can journalism survive the end of newspapers?’ and that’s what worries me most.

“I’m not so worried about the platform our work appears on, but I’m afraid that we are running down the numbers of journalists across Britain and professional journalists are essential for the health of any democracy.”